Presently, if memory, such as a CD, DVD or hard drive, detects a severe reading error at a particular location in the memory, it informs the host software and the host software will not use that spot again. The host remaps the memory to an alternate location as controlled by its sparing table marking the spot as bad. The memory then places new data that would have been directed to the trouble location in its sparing table. When it is desired to read data from the spot that is bad, instead of reading that spot, the memory will read the data stored at a specific area in the sparing table.
Thus, if there is a fingerprint or smudge or something on the disc, or if the disc is scratched or worn at a spot, the disc marks the trouble area as a bad area and then rewrites the data from that area to a new area. Two different situations can occur. One is contamination or errors that are temporary are those that may be removed by cleaning the disc or by doing something to the disc; and the other is a permanent defect like a scratch or the wearout mechanism of the disc that is not recoverable. Current systems treat these two cases identically since they cannot tell the difference between a fingerprint, a piece of dust, a scratch, or the wearing out of a piece of the media. In either case, the memory tells the software that it had trouble reading a particular spot and directs the software to map that spot as bad. Thus, once a spot is marked as bad it is never reused, even if, for instance, the disc is cleaned and the smudge is removed.